Steering device

Abstract

The present application relates to a steering device that steers a tire (99) in a vehicle of a steer-by-wire system (90) in which a steering operation mechanism and a steering mechanism are mechanically separated, the steering device having a steering unit (80) that includes a steering actuator (88) and a steering angle control device (85). The steering actuator (88) steers the tire (99) in accordance with an instructed steering angle. The steering angle control device (85) calculates a steering angle command value (θ * t) corresponding to an input steering operation angle (θr) signal, and generates a signal that drives the steering actuator (88) on the basis of the steering angle command value. The steering angle control device (85) performs a restriction such that an absolute value of a steering angle velocity is below a steering angle velocity limit value (ωt_lim) set in accordance with a prescribed parameter.

Description

[0001] Cross-references to related applications

[0002] This application incorporates the contents of Japanese Patent Application No. 2020-177252, filed on October 22, 2020. Technical Field

[0003] This disclosure relates to steering mechanisms. Background Technology

[0004] Previously, there were known techniques for making the steering angular velocity variable in vehicles with steer-by-wire systems where the steering control mechanism and the steering mechanism were mechanically separated. For example, the device disclosed in Patent Document 1 calculates an optimal steering angular velocity smaller than the original one by multiplying the original steering angular velocity by a gain that depends on the steering control angle and vehicle speed, thereby optimizing the response speed of the steering wheel in accordance with the steering wheel operation state.

[0005] Patent Document 1: Japanese Patent No. 5966684

[0006] In a steering-by-wire system, the ratio of the steering angle to the steering control angle, i.e., the steering angle ratio, can be variably set. However, if steering is performed with the same feel at a high steering angle ratio as at a low steering angle ratio, the tires will turn at a speed higher than expected. Therefore, in the prior art of Patent Document 1, there is a problem: significant vehicle behavior such as roll and yaw occurs during cornering at a high steering angle ratio, resulting in a deterioration in ride comfort. Summary of the Invention

[0007] The purpose of this disclosure is to provide a steering device that, in a vehicle with a steer-by-wire system, suppresses vehicle behavior during cornering maneuvers and improves ride comfort. Here, the vehicles with steer-by-wire systems envisioned in this disclosure are not limited to vehicles operated by a driver, but also include autonomous vehicles.

[0008] This disclosure relates to a steering device for steering the tires in a vehicle with a steer-by-wire system where the steering control mechanism and the steering mechanism are mechanically separated. It includes a steering device for use in autonomous vehicles, at least comprising a steering unit including a steering actuator and a steering angle control device.

[0009] The steering actuator steers the tires according to the indicated steering angle. The steering angle control device calculates a steering angle command value corresponding to the input steering angle signal and generates a signal to drive the steering actuator based on this steering angle command value. The steering angle control device limits the absolute value of the steering angular velocity to below a steering angular velocity limit value set according to prescribed parameters.

[0010] Furthermore, the steering system of a vehicle using a steer-by-wire system for driver operation also includes a reaction force device comprising a reaction force actuator and a reaction force control device. The reaction force actuator applies a reaction force to the steering wheel in response to the driver's steering input. The reaction force control device generates a signal to drive the reaction force actuator based on a signal from the steering angle control device.

[0011] For example, as a "prescribed parameter," the steering angle control device changes the steering angle speed limit value based on the equivalent value of the steering angle or the equivalent value of the steering control angle, vehicle behavior, vehicle speed, and the state of turning in or out. Here, the "equivalent value of the steering angle" or the "equivalent value of the steering control angle" can be the steering angle or the steering control angle itself, or it can be any value related to the steering angle or the steering control angle. The indicated value in autonomous driving is also included here. "Turning in or out" is not limited to the driver's driving operation, but is interpreted more broadly as the change in steering direction based on the indicated value in autonomous driving.

[0012] In a steer-by-wire system where the tires steer proportionally to the steering angle, the vehicle behavior (specifically, roll angle) generated during steering is proportional to the yaw angle, yaw rate, and the time rate of change of the tire slip angle. Therefore, in this disclosure, by limiting the steering rate, vehicle behavior during cornering can be suppressed, improving ride comfort. Roll is particularly suppressed during cornering at high steering ratios. Attached Figure Description

[0013] The above-mentioned objects, as well as other objects, features, and advantages of the present invention, become more apparent from the accompanying drawings and the detailed description below. The accompanying drawings are...

[0014] Figure 1 This is an overall structural diagram of a steer-by-wire system that applies one embodiment of the steering device.

[0015] Figure 2 This is a block diagram of a steering device according to one embodiment.

[0016] Figure 3 This is a time graph showing the occurrence of body roll during turning in the comparative example.

[0017] Figure 4 This is a frontal view of a vehicle illustrating the relationship between roll angle and roll moment.

[0018] Figure 5 This is a control block diagram of the reaction force device and the steering unit.

[0019] Figure 6 This is a block diagram representing an example of setting the steering angle velocity limit value for steering angle response.

[0020] Figure 7 This is a block diagram representing a setting example of the steering angle and vehicle speed response steering angle speed limit value.

[0021] Figure 8 This is a block diagram illustrating a setting example of the steering angular velocity limit value based on the turn-in / turn-out determination.

[0022] Figure 9 This is a block diagram representing a structural example of a steering angle command value limit.

[0023] Figure 10 This is a block diagram of the steering angle ratio control example 1, which represents the steering angle and vehicle speed response.

[0024] Figure 11 This is a block diagram of the steering angle ratio control example 2, which represents the steering angle and vehicle speed response.

[0025] Figure 12 This is a timeline illustrating the roll suppression effect based on steering angular velocity limits.

[0026] Figure 13 This is a graph showing the relationship between the remaining angle to the end and the steering angular velocity limit value in an embodiment where the angle error based on the steering angular velocity limit is below the allowable angle error. Detailed Implementation

[0027] (One implementation method)

[0028] One embodiment of the steering device will be described with reference to the accompanying drawings. This steering device is a means of steering the tires in a vehicle with a steer-by-wire system where the steering control mechanism and the steering mechanism are mechanically separated. In one embodiment, a steering device is envisioned for use in a vehicle with a steer-by-wire system where the driver performs driving operations. Furthermore, as described in the section on other embodiments, this steering device can also be used in autonomous vehicles.

[0029] exist Figure 1 The diagram shows the overall structure of the steer-by-wire system 90. Figure 1 In the diagram, only one side of tire 99 is shown; the tire on the opposite side is omitted. The steering system 10 includes a reaction force device 70 and a steering unit 80.

[0030] The reaction force device 70 includes a reaction force actuator 78 and a reaction force control device 75 that generates a signal to drive the reaction force actuator 78. It is connected to the steering wheel 91 via a reaction force reducer 79 and a steering shaft 92. The steering wheel 91 is the mechanism for inputting the steering angle; typically a steering wheel, but it can also be a steering lever or similar shape. In the steering-by-wire system 90, the driver cannot directly perceive the reaction force applied to steering input. Therefore, the reaction force actuator 78 rotates the steering wheel 91 to apply a reaction force to steering input, providing the driver with an appropriate steering feel.

[0031] The steering unit 80 includes a steering actuator 88 and a steering angle control device 85 that generates signals to drive the steering actuator 88. The rotation of the steering actuator 88 is transmitted from a steering reducer 89 to the tire 99 via a pinion 96, rack and pinion shaft 97, tie rod 98, and steering knuckle arm 985. Specifically, the rotational motion of the pinion 96 is converted into linear motion of the rack and pinion shaft 97, and the tie rods 98 located at both ends of the rack and pinion shaft 97 cause the steering knuckle arm 985 to reciprocate, thereby steering the tire 99.

[0032] The torque sensor 94 detects the driver's steering input applied to the steering shaft 92 based on the torsional displacement of the torsion bar. The detected value T_sns by the torque sensor 94 is input to the reaction force control device 75.

[0033] The steering angle of the steering wheel 91 is determined by the direction of rotation of the steering wheel 91 relative to the neutral position, for example... Figure 1 The CW direction is defined as positive, and the CCW direction is defined as negative. Correspondingly, the steering angle of the tire 99 is defined as positive or negative. Angular velocity is defined with the same sign as angle. Additionally, the torque sensor 94 detects a positive value T_sns when the driver turns the steering wheel 91 in the CW direction.

[0034] Furthermore, the output torque of the reaction force device 70 is also positive when the steering wheel 91 is turned in the CW direction by the reaction force device 70. When the output torque of the reaction force device 70 acts in the CW direction, if the driver maintains the steering state of the steering wheel 91, torque is applied in the CCW direction. Therefore, the detection value T_sns of the torque sensor 94 is negative.

[0035] The reaction force control device 75 and the steering angle control device 85 are mainly composed of a microcomputer, etc., and internally include a CPU, ROM, RAM, I / O, and buses connecting these structures (not shown). The processing of the reaction force control device 75 and the steering angle control device 85 can be based on software processing by executing pre-stored programs through the CPU, or it can be hardware processing performed by dedicated electronic circuits. The reaction force control device 75 and the steering angle control device 85 communicate with each other via vehicle networks such as CAN communication or dedicated communication lines.

[0036] Reference Figure 2 The structure of the steering device 10 in the steer-by-wire system 90 will be described. The reaction force device 70 includes a reaction force control device 75, a steering angle sensor 76, and a reaction force actuator 78. The steering angle sensor 76 detects the steering angle θr input from the steering wheel 91. The reaction force control device 75 generates a reaction force signal to drive the reaction force actuator 78 based on the signal from the steering angle control device 85. The reaction force actuator 78 applies a reaction force to the steering wheel 91 in response to the driver's steering input.

[0037] The steering unit 80 includes a steering angle control device 85, a steering angle sensor 86, and a steering actuator 88. The steering angle control device 85 calculates the steering angle command value θ corresponding to the input steering angle θr. * t, based on the steering angle command value θ * A signal is generated to drive the steering actuator 88. The steering actuator 88 steers the tire 99 according to the indicated steering angle. The steering angle θt is controlled by feedback from the steering angle sensor 86. Alternatively, depending on the situation, the reaction force of the reaction force actuator 78 can be calculated based on the current feedback from the steering actuator 88.

[0038] The steering system 10 basically controls the steering angle θt freely based on the steering input angle θr. Furthermore, during steering, a reaction force is applied to the steering wheel 91 using the current value generated in the steering actuator 88, etc. In this specification, the ratio of the steering angle θt to the steering input angle θr is defined as the "steering angle ratio". A high steering angle ratio allows for a larger steering angle with a smaller steering input angle. Generally, a high steering angle ratio is used in the low-speed range to reduce steering input, while a low steering angle ratio is used in the high-speed range for vehicle stability.

[0039] Furthermore, in this embodiment, the vehicle speed V detected by the vehicle speed sensor 81 is input to the reaction force control device 75 and the steering angle control device 85. In addition, parameters representing vehicle behaviors such as roll and yaw are input from the vehicle behavior detection device 82 to the steering angle control device 85.

[0040] Here, the technical background of this embodiment will be explained. One advantage of the steer-by-wire system compared to an electric power steering system where the steering control mechanism and the steering mechanism are mechanically combined is that the steering angle ratio can be variably set according to the situation. At a high steering angle ratio, the steering angle can be rotated to the maximum steering angle with a smaller steering control angle, allowing the driver to drive without switching hands on the steering wheel 91. Therefore, since the driver can perform parking, U-turns, etc., with a smaller steering control angle, the steering load is reduced.

[0041] On the other hand, refer to Figure 3 , Figure 4 This section explains the instability in vehicle behavior during cornering at high steering angle ratios. Figure 3 The diagram shows the time variations of the steering angle θt, steering angular velocity ωt, and roll angular velocity when performing steering maneuvers to make a U-turn from straight-line driving. Values ​​other than "0" are omitted on the vertical axis; the units in parentheses are used solely to represent the dimensions of each quantity.

[0042] Steering control begins at approximately 3.0 seconds and ends at approximately 3.8 seconds. During this period, the steering angular velocity ωt increases from 0. After steering control ends, as indicated by the * mark, significant body roll occurs in the left-right direction. This results in significant vehicle behavior such as body roll and yaw during cornering at high steering ratios, leading to a deterioration in ride comfort.

[0043] Reference Figure 4 Regarding the roll angle generated during a left turn The roll moment at this time will be explained (reference: Masato Abe, "Motion and Control of Automobiles: The Theory Formation and Application of Vehicle Kinematics" [2nd ed.]). The roll moment is represented by the following equation (1). The left side <1> represents the roll stiffness, <2> represents the center of gravity offset torque, and <3> represents the roll damping. The right side <4> represents the "inertial moment of roll angular acceleration", and <5> represents the "moment related to yaw".

[0044] [Formula 1]

[0045]

[0046]

[0047] As important factors of roll, roll stiffness, roll damping, roll angular acceleration relative to the moment of inertia, yaw angle, yaw angular velocity, and the differential value of tire slip angle (i.e., the rate of change over time) have an impact.

[0048] The key point here is "yawing-related moments." At high steering ratios, the increase in steering speed accompanying the steering input speed is greater. Compared to the inertial moment of roll acceleration, the influence of the yawing angle, yawing rate, and the derivative of the tire slip angle is considered to be more significant. In the low-speed range, the yawing angle and yawing rate are considered to be proportional to the steering angle and steering rate; therefore, it is hypothesized that limiting the steering rate can suppress roll.

[0049] Furthermore, instead of yaw angle and yaw rate, roll suppression effects can also be derived by adjusting roll stiffness and roll damping. Japanese Patent No. 5416442 discloses a suspension control device that optimizes the responsiveness to steering maneuvers based on this viewpoint. However, changing the suspension parameters requires four special suspension components, leading to increased costs. In contrast, the method for limiting steering rate only requires changing the control mechanism, without increasing costs.

[0050] Therefore, in this embodiment, in order to suppress body roll during cornering operations, especially at high steering angle ratios, a module for limiting the steering angular velocity of the steering actuator 88 is provided in the steering unit 80. Next, referring to... Figure 5 The detailed control structure of the steering device 10 according to one embodiment will be described. The parameter related to the output of the reaction force device 70 is marked with the symbol "r", and the parameter related to the output of the steering unit 80 is marked with the symbol "t".

[0051] Here, the values ​​of steering angle θr, steering angular velocity ωr, and steering angle θr are interpreted as "equivalent values" that include the rotation angle and angular velocity of the reaction force actuator 78 or steering actuator 88, appropriately multiplied by the reduction ratio of the reducers 79 and 89. Furthermore, the "steering torque Tt," which directly represents the output torque of the steering actuator 88, is interpreted as including the steering torque command value T. * t, the current It flowing through the steering actuator 88 or the current command value I * The "equivalent value" of t, etc.

[0052] The reaction force control device 75 of the reaction force device 70 includes a reaction force control unit 51, a viscous control unit 52, an inertial control unit 53, a return control unit 54, a torque deviation calculation unit 66, a PID controller 67, and a current control unit 68. The reaction force control unit 51 calculates the steering torque command value T after adjusting for increases or decreases based on the steering torque equivalent value Tt at vehicle speed V. * st.

[0053] The viscous control unit 52 calculates a viscous command value Tvisc that is approximately proportional to the equivalent value of the steering angular velocity ωr. Alternatively, it may be referred to as the "friction control unit" instead of the "viscous control unit". The inertial control unit 53 calculates an inertial command value Tinert that is approximately proportional to the derivative of the equivalent value of the steering angular velocity ωr (i.e., the equivalent value of the steering angular acceleration). The return control unit 54 calculates a return command value Tret based on the equivalent value of the steering angular velocity θr, the equivalent value of the steering angular velocity ωr, and the vehicle speed V, acting in the direction that returns the steering wheel 91 to the neutral position.

[0054] In adders 552, 553, and 554, the steering torque command value T is... * The sign inversion of st (-T) * st) Add the viscous command value Tvisc, the inertia command value Tinert, and the return command value Tret in sequence. The sum of these values ​​using adder 554 is used as the "steering torque command value T". * The target value of st is T ** "st" is output.

[0055] Torque deviation calculation unit 66 calculates target value T ** The torque deviation ΔT between the measured value T_sns and the measured value T_sns by the torque sensor 94 is controlled by the PID controller 67. This PID controller makes the torque deviation ΔT approach 0, i.e., makes the measured value T_sns by the torque sensor 94 follow the target value T. ** st, and calculate the current command value I * r. The current control unit 68 controls the current Ir flowing through the reaction force actuator 78. The steering angle equivalent value θr, which is the rotation angle of the reaction force actuator 78, is detected by the steering angle sensor 76 and output to the return control unit 54 of the reaction force control device 75 and the steering angle control device 85.

[0056] The steering angle control device 85 of the steering unit 80 includes a steering angle ratio control unit 320, a filter 33, a steering angle velocity limit setting unit 340, a steering angle velocity limit unit 350, an angle deviation calculation unit 36, a PID controller 37, and a current control unit 38.

[0057] The steering angle ratio control unit 320 calculates the ratio of the steering angle θt to the steering angle θr, i.e., the steering angle ratio RA, based on the equivalent value of the steering control angle θr and the vehicle speed V. It then multiplies the steering control angle θr by the steering angle ratio RA to calculate the steering angle command value θ before limiting the steering angle. * t_0. For a specific example of steering angle ratio control, please refer to [reference needed]. Figure 10 , Figure 11The process will be described later. The forward steering angle command value θ is limited by a filter 33 consisting of a notch filter to avoid resonance and an LPF to avoid steep input. * t_0.

[0058] The steering angular velocity limit setting unit 340 changes the steering angular velocity limit value ωt_lim according to prescribed parameters. The "prescribed parameters" include the equivalent value of steering angle θr or steering angle θt, vehicle speed V, vehicle behavior such as yaw or roll, and the state of turning in or out. For specific examples of changing the steering angular velocity limit value ωt_lim according to each parameter, please refer to... Figures 6-8 This will be discussed later. Furthermore, while illustrations for examples of vehicle behavior response are omitted, real-time control is possible by varying the limit value ωt_lim according to parameters of vehicle behavior.

[0059] The steering angular velocity limiting unit 350 limits the absolute value of the steering angular velocity to below the steering angular velocity limit value ωt_lim. For a specific example of the steering angle command value limitation based on the steering angular velocity limit, please refer to... Figure 9 As will be discussed later. Additionally, as indicated by the thick arrow, when a steering angular velocity limit is applied, the constant value of the reaction force control device 75 can be switched, increasing the reaction force applied to the reaction force actuator 78. This allows the driver to physically suppress the steering input speed.

[0060] Specifically, in the reaction force control unit 51, a constant for reaction force control proportional to the steering torque value Tt can be switched to increase the reaction force when a steering angular velocity limit is applied. Alternatively, in the viscosity control unit 52 and the inertia control unit 53, when a steering angular velocity limit is applied, the constants of friction control and inertia control originally used to construct steering feel can be switched to increase the reaction force, or the constants of friction control and inertia control originally used to construct steering feel can be made consistent to increase the reaction force.

[0061] Steering angle deviation calculation unit 36 ​​calculates the steering angle command value θ * The angle deviation Δθt between t and the steering angle feedback value θt. The PID controller 37 performs PID control to make the angle deviation Δθt approach 0, and calculates the current command value I. * The current control unit 38 controls the current It flowing through the steering actuator 88. The steering angle equivalent value θt, which corresponds to the rotation angle of the steering actuator 88, is detected by the steering angle sensor 86 and fed back to the steering angle deviation calculation unit 36. In addition, the steering torque equivalent value Tt is output to the reaction force control device 75.

[0062] Next, refer to Figures 6 to 11The control examples for each box are explained. In each diagram, for convenience, the input and output characteristics of the parameters are described based on "mapping," but they can also be implemented through arithmetic calculations.

[0063] First, regarding the structural example of the steering angular velocity limit setting unit 340, refer to... Figures 6-8 . Figure 6 In the example, the steering angular velocity limit setting unit 340 defines a steering angular velocity limit value ωt_lim for the absolute value of the steering angle θt using a steering angle response mapping 341. For example, in the region where the absolute value of the steering angle θt is below θα, the limit value ωt_lim is set to a relatively high value ωtH, and in the region where the absolute value of the steering angle θt is above θβ (>θα), the limit value ωt_lim is set to a relatively low value ωtL. In the region where the absolute value of the steering angle θt is between θα and θβ, the limit value ωt_lim gradually decreases from a higher value ωtH to a lower value ωtL. Thus, when the absolute value of the steering angle θt is greater than a certain value, steering at an angular velocity higher than the limit value ωt_lim is prevented.

[0064] The input to the steering angle response map 341 can be either the steering angle detection value θt detected by the steering angle sensor 86 or the steering angle command value θ. * t or other "equivalent steering angle value". Alternatively, the steering angle θr or "equivalent steering angle value" before multiplying by the steering angle ratio RA can also be used as input. The following sections related to steering angle response are all explained in the same way.

[0065] By varying the steering angular velocity limit ωt_lim according to the equivalent value of the steering angle or the steering control angle, rapid steering in the small steering angle region and smooth steering in the large steering angle region can be achieved. Therefore, the effect of yaw in the small steering angle region, where roll behavior is unlikely, can be reduced. Furthermore, Figure 6 The steering angle response mapping 341 is based on the values ​​ωtH and ωtL of two stages, and the limit value ωt_lim changes linearly according to the steering angle. However, it can also be based on the values ​​of three or more stages, and the limit value ωt_lim can also change curve according to the steering angle.

[0066] exist Figure 7 In the examples, besides with Figure 6In addition to the same steering angle response mapping 341, a vehicle speed gain mapping 343 is also used. For example, the vehicle speed gain is 1 in the region below vehicle speed Vα, gradually increases from 1 in the region from vehicle speed Vα to vehicle speed Vβ, and is set to a value INF that is sufficiently large than 1 in the region above vehicle speed Vβ. The multiplier 344 multiplies the temporary limit value ωt_lim_0 calculated by the steering angle response mapping 341 by the vehicle speed gain to calculate the steering angular velocity limit value ωt_lim. When the vehicle speed gain is a sufficiently large value INF, the steering angular velocity limit is essentially not applied.

[0067] In areas with high vehicle speeds (V), the steering angle is already relatively small, so further limiting the steering angle rate would increase steering delay. Conversely, since large steering movements are not expected in high-speed areas, steering angle rate limiting is unnecessary. Therefore, according to... Figure 7 That structure, by limiting the steering angular velocity ωt in the low-speed region and not limiting it in the high-speed region, enables rapid steering in the high-speed region.

[0068] Figure 8 The example steering angular velocity limit setting unit 340 includes steering angle response maps 342F and 342R for turning in and turning out, which have different steering angle response characteristics, and a switch 345, which changes the steering angular velocity limit value ωt_lim according to the turning in or turning out state. The limit value ωt_lim_R of the turning-out steering angle response map 342R is set smaller than the limit value ωt_lim_F of the turning in steering angle response map 342F. During cornering, because energy is stored in the suspension springs, the vehicle body is more prone to swaying when turning out compared to when turning in. Therefore, by making the limit value ωt_lim_R when turning out smaller than the limit value ωt_lim_F when turning in, more stable vehicle behavior is achieved.

[0069] The switch 345 selects either the limit value ωt_lim_F for turning in or the limit value ωt_lim_R for turning out, based on the signal from the turn-in / turn-out determination unit 41. Here, there are, for example, three methods for determining turn-in / turn-out. The first method is based on the signs of the steering angle θr and the steering angular velocity ωr. The second method is based on the signs of the steering angular velocity ωr and the steering torque during turn-in / turn-out (i.e., during steering operation). These are also commonly used in electric power steering systems.

[0070] The third method is unique to steer-by-wire systems, focusing on the difference between the reaction torque Tr output from the reaction force actuator 78 and the detection value T_sns of the torque sensor 94, caused by the torque loss due to the gears of the reducer 79. When the steering wheel 91 is turned in by the driver, the absolute value of the detection value T_sns of the torque sensor 94 is greater than the absolute value of the reaction torque Tr. Conversely, when the steering wheel 91 is turned back by the reaction force actuator 78, the absolute value of the detection value T_sns of the torque sensor 94 is smaller than the absolute value of the reaction torque Tr.

[0071] Next, refer to Figure 9 The structure of the steering angle command value limiting unit 350 will be described below. Delay elements 352 and 355 limit the steering angle command value θ. ** The previous value of t is output to the angular velocity calculator 351 and the adder 354, respectively. The angular velocity calculator 351 limits the forward steering angle command value θ. * t_0 and the steering angle command value θ after limitation ** The difference between the previous value of t is used to calculate the steering angular velocity ωt_0 before the limit. Absolute value protection mapping 353 protects the absolute value of the steering angular velocity ωt to the steering angular velocity limit value ωt_lim.

[0072] Adder 354 adds the limited steering angular velocity ωt to the limited steering angle command value θ. ** The previous value of t, outputting the steering angle command value θ after limiting. ** The current value of t. Additionally, a filter can be added to the current value output to smooth out the change. Furthermore, to alleviate the discomfort associated with steering angular velocity limitation, the steering angular velocity limit value ωt_lim can be changed based on the duration of the limitation and the steering torque.

[0073] Next, refer to Figure 10 , Figure 11 The structure of the steering angle ratio control will be described below. The steering angle control device 85 can also limit the steering angular velocity ωt by making the steering angle ratio RA change according to the steering control angle θr. Regarding the input of the steering angle response in this case, either the steering control angle equivalent value or the steering angle equivalent value can be used.

[0074] Figure 10The steering angle ratio control unit 320 of the shown steering angle ratio control example 1 includes steering angle response maps 321 and 322, a vehicle speed gain map 325, a multiplier 326, an adder 327, and a multiplier 328. The steering angle response map 321 calculates the steering angle response term RA(θ) corresponding to the absolute value of the steering angle θr. The steering angle response map 322 calculates the reference value RA(V)_0 of the vehicle speed response term corresponding to the absolute value of the steering angle θr. The vehicle speed gain map 325 and... Figure 7 The mapping 343 calculates the vehicle speed gain corresponding to the vehicle speed V in the same way. The multiplier 326 multiplies the reference value RA(V)_0 of the vehicle speed response term by the vehicle speed gain to calculate the vehicle speed response term RA(V).

[0075] Adder 327 adds the steering angle response term RA(θ) and the vehicle speed response term RA(V) to calculate the steering angle ratio RA. Multiplier 328 multiplies the steering angle θr by the steering angle ratio RA to calculate the steering angle command value θ before limiting. * t_0.

[0076] In the steering angle ratio control example 1, the steering angle ratio RA is set relatively small near the neutral position where the absolute value of the steering angle θr is 0, and relatively large in the region where the absolute value of the steering angle θr is large. In this case, since the steering angular velocity ωt is large in the latter half of the turn-in operation, a steering angular velocity limiter in the additional steering angular velocity limiter 350 is required.

[0077] Figure 11 The steering angle ratio control unit 320 shown in the steering angle ratio control example 2 is relative to Figure 10 The structures are identical except for the characteristics of the steering angle response mappings 323 and 324. In steering angle ratio control example 2, unlike steering angle ratio control example 1, the steering angle ratio RA is set relatively high near the neutral position and relatively low in the region where the absolute value of the steering angle θr is large. In this case, since the steering angle velocity ωt is small in the latter half of the turn operation, the steering angle velocity limit in the steering angle velocity limiter 350 is not required. However, the stability during straight-line driving is reduced.

[0078] (Effect)

[0079] As described above, in this embodiment, by limiting the steering angular velocity ωt, vehicle behavior during cornering can be suppressed, improving ride comfort. In particular, body roll can be suppressed during cornering at high steering angle ratios. Figure 12 The simulation analysis results shown relate to the effect of limiting the roll rate ωt on the yaw rate. Figure 12 In the middle, the dashed line is Figure 3The waveform shown is before the steering angular velocity is limited, and the solid line is the waveform after the steering angular velocity is limited.

[0080] After steering control begins, the steering angular velocity ωt reaches the steering angular velocity limit value ωt_lim at time ta, and the limitation begins. Steering control ends at time tb, but since the steering angle θt has not reached the target value θt_tgt, the output of the steering angular velocity ωt is extended and continues until time tc. At this time, the integral value S1 of the steering angular velocity ωt reduced during the limitation from time ta to time tb is equal to the integral value S2 of the steering angular velocity ωt added during the extension from time tb to time tc. As a result, the steering angle θt at time tc reaches the target value θt_tgt. By limiting the steering angular velocity ωt in this way, the roll rate generated in the vehicle, which appears in the *marked part of the waveform before limitation, is reduced.

[0081] However, by limiting the steering angular velocity, an angular error is introduced between the anticipated steering angle, which is proportional to the original steering control angle θr, and the actual steering angle θt. This can result in a significant angular deviation from the neutral position to the end position. Figure 12 In the example, in order to compensate for the angle error θerr generated at time tb, the driver continues to turn until time tc after the steering operation ends, which raises concerns about causing discomfort to the driver.

[0082] Therefore, refer to Figure 13 The following embodiments will be described to limit the steering angular velocity so that the angle error θerr caused by the steering angular velocity limit is within the specified allowable angle error θerr_th. Figure 13 The horizontal axis represents the absolute value of the difference between the current steering angle θt or steering control angle θr and the corresponding limit angle of the mechanical end effector, also known as the "remaining angle θrest". With each steering maneuver, the remaining angle θrest decreases from its maximum value θN in the neutral position to a value of 0 at the end effector. Figure 13 In the vertical axis, the maximum value of the steering angular velocity ωt_max is the steering angular velocity equivalent to the maximum value of the driver's operating speed.

[0083] The steering angle control device 85 determines the steering angle control device based on the remaining angle θrest. The smaller the remaining angle θrest, the smaller the steering angle velocity limit ωt_lim, so that the angle error θerr from the neutral position to the end is kept constant and is the allowable angle error θerr_th. The relationship between the remaining angle θrest and the allowable angle error θerr_th is expressed by equation (2).

[0084] [Equation 2]

[0085]

[0086] In the formula, the limit index value represented by "(ωt_max-ωt_lim) / ωt_lim" is smaller when the steering angle limit is more relaxed near the neutral position, and larger when the limit is more strict near the end. If we rearrange the formula (2), we can obtain the formula (3) for the steering angle velocity limit value ωt_lim.

[0087] [Formula 3]

[0088]

[0089] According to equation (3), when “θrest=θerr_th”, “ωt_lim=ωt_max / 2” is derived. That is, the allowable angle error θerr_th is equivalent to the remaining angle θrest when the steering angular velocity limit value ωt_lim is set to (1 / 2) of the imagined maximum steering angular velocity value ωt_max.

[0090] In this embodiment, the impact of the angle error caused by the steering angle velocity limit during steering on the driver can be reduced. Therefore, it is possible to appropriately balance the effect of the steering angle velocity limit on suppressing vehicle behavior during cornering and the effect of the steering angle deviation on eliminating discomfort. Furthermore, the steering angle velocity limit value ωt_lim is not limited to being calculated by the above formula (3), but can also be calculated by other formulas, mappings, etc.

[0091] (Other implementation methods)

[0092] (a) The steering device 10 of the above embodiment is envisioned for use in vehicles with steer-by-wire systems where the driver performs driving operations, and includes a reaction force device 70 and a steering unit 80. The same applies to vehicles capable of switching between manual and automatic driving. On the other hand, in the case of vehicles with steer-by-wire systems that are used in fully automatic driving systems, the steering device may not include the reaction force device 70 and may only include the steering unit 80.

[0093] In this case, by inputting the steering angle θr calculated by the automatic driving control device to the steering unit 80, the steering unit 80 can perform the same control as in the above-described embodiment. Furthermore, it is not necessary to... Figure 5 As shown by the thick arrow, the constant control of the reaction force control device 75 is switched when the steering angular velocity limit is applied.

[0094] (b) in Figures 6-8In this example, the parameters used to set the steering angular velocity limit ωt_lim are only combinations of a subset of the following parameters: steering angle equivalent θr or steering angle equivalent θt, vehicle speed V, vehicle behavior, and the state of turning in or out. Furthermore, these parameters can be used in appropriate combinations. In this case, the priority and weighting of the effects of each parameter can also be set.

[0095] This disclosure is not limited to such implementations and can be implemented in various ways without departing from its spirit.

[0096] The control device and method described in this disclosure can also be implemented using a dedicated computer, which is provided by comprising a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control device and method described in this disclosure can also be implemented using a dedicated computer provided by employing one or more dedicated hardware logic circuits to construct a processor. Alternatively, the control device and method described in this disclosure can also be implemented using one or more dedicated computers, which are composed of a combination of a processor and memory programmed to perform one or more functions, and a processor composed of one or more hardware logic circuits. Furthermore, the computer program can also be stored as instructions to be executed by the computer on a computer-readable non-transferable tangible recording medium.

[0097] This disclosure is described based on embodiments. However, this disclosure is not limited to these embodiments and structures. This disclosure also includes various modifications and equivalent variations. In addition, various combinations and methods, further including only one of their elements, or other combinations and methods with more or fewer elements, are also included in the scope and spirit of this disclosure.

Claims

1. A steering device, in a vehicle with a steer-by-wire system where the steering control mechanism and the steering mechanism are mechanically separated, for steering the tires, wherein... The aforementioned steering device includes a steering unit comprising a steering actuator and a steering angle control device. The steering actuator steers the tires according to an indicated steering angle. The steering angle control device calculates a steering angle command value corresponding to an input steering angle signal and generates a signal to drive the steering actuator based on the steering angle command value. The aforementioned steering angle control device limits the absolute value of the steering angular velocity to below a steering angular velocity limit set according to prescribed parameters. The aforementioned steering angle control device adjusts the steering angle speed limit value based on the remaining angle. The smaller the remaining angle, the smaller the steering angle speed limit value, so that the angle error caused by the steering angle speed limit is below the specified allowable angle error. The remaining angle is the absolute value of the difference between the current steering angle or steering control angle and the corresponding mechanical end limit angle.

2. The steering device according to claim 1, wherein, Vehicles using steer-by-wire systems for driving operations. It also includes a reaction force device comprising a reaction force actuator and a reaction force control device, wherein the reaction force actuator applies a reaction force to the steering wheel in response to the driver's steering operation, and the reaction force control device generates a signal to drive the reaction force actuator based on a signal from the steering angle control device.

3. The steering device according to claim 1, wherein, The aforementioned steering angle control device changes the aforementioned steering angular velocity limit value based on the equivalent value of the steering angle or the equivalent value of the steering control angle.

4. The steering device according to any one of claims 1 to 3, wherein, The aforementioned steering angle control device changes the aforementioned steering angle speed limit value according to the vehicle's behavior.

5. The steering device according to any one of claims 1 to 3, wherein, The aforementioned steering angle control device changes the aforementioned steering angle speed limit value according to the vehicle speed.

6. The steering device according to any one of claims 1 to 3, wherein, The aforementioned steering angle control device changes the aforementioned steering angular velocity limit value according to the state of turning in or turning out.

7. The steering device according to any one of claims 1 to 3, wherein, The aforementioned steering angle control device changes the ratio of the steering angle to the steering control angle, i.e., the steering angle ratio, based on the equivalent value of the steering control angle or the equivalent value of the steering angle.

8. A steering device, in a vehicle with a steer-by-wire system where the steering control mechanism and the steering mechanism are mechanically separated, for steering the tires, wherein... The aforementioned steering device includes a steering unit comprising a steering actuator and a steering angle control device. The steering actuator steers the tires according to an indicated steering angle. The steering angle control device calculates a steering angle command value corresponding to an input steering angle signal and generates a signal to drive the steering actuator based on the steering angle command value. The aforementioned steering angle control device limits the absolute value of the steering angular velocity to below a steering angular velocity limit set according to prescribed parameters. The aforementioned steering angle control device changes the aforementioned steering angular velocity limit value according to the state of turning in or turning out. The aforementioned steering angular velocity limit value during the turn-back is less than the aforementioned steering angular velocity limit value during the turn-in.

9. A steering device, in a vehicle with a steer-by-wire system where the steering control mechanism and the steering mechanism are mechanically separated, for steering the tires, wherein... The aforementioned steering device includes a steering unit comprising a steering actuator and a steering angle control device. The steering actuator steers the tires according to an indicated steering angle. The steering angle control device calculates a steering angle command value corresponding to an input steering angle signal and generates a signal to drive the steering actuator based on the steering angle command value. The aforementioned steering angle control device limits the absolute value of the steering angular velocity to below a steering angular velocity limit set according to prescribed parameters. The aforementioned steering angle control device determines whether to turn in or out based on the reaction force torque and the detection value of the torque sensor.

10. A steering device, in a vehicle with a steer-by-wire system where the steering control mechanism and the steering mechanism are mechanically separated, for steering the tires, wherein... The aforementioned steering device includes a steering unit comprising a steering actuator and a steering angle control device. The steering actuator steers the tires according to an indicated steering angle. The steering angle control device calculates a steering angle command value corresponding to an input steering angle signal and generates a signal to drive the steering actuator based on the steering angle command value. The aforementioned steering angle control device limits the absolute value of the steering angular velocity to below a steering angular velocity limit set according to prescribed parameters. The aforementioned steering mechanism is used in vehicles with steer-by-wire systems where the driver performs driving operations. The aforementioned steering system further includes a reaction force device comprising a reaction force actuator and a reaction force control device. The reaction force actuator applies a reaction force to the steering wheel in response to the driver's steering input. The reaction force control device generates a signal to drive the reaction force actuator based on a signal from the steering angle control device. When the steering angle control device imposes a limit on the steering angular velocity, the reaction force device switches the constant of the reaction force control device or makes the constant of the friction control device consistent with the constant of the inertial control device, so as to increase the reaction force.

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